It is known that conventional power supplies can be used to convert AC power into DC power.
A drawback of converting AC power into DC power is that a corresponding AC/DC converter, if not designed properly, can inject unwanted harmonic frequencies into the AC line (input current). Certain regulatory agencies limit the degree to which harmonic frequencies can be injected in the line voltage because injection of too many harmonics can be harmful to operation of other devices that use the AC line voltage.
In comparison to the resistive type of loads used fifty years ago, conventional electronic equipment such as, computers, servers, data storage devices, etc., tends to be more reactive. Such conventional electronic equipment can therefore cause an unwanted phase displacement between the line voltage and corresponding input current. When powering a resistive load, there is little or no phase displacement. When powering a reactive load, there can be substantial phase displacement resulting in poor conversion efficiency.
In general, a so-called power factor of an AC/DC converter represents a ratio of real power to apparent power. The power factor is typically defined as a number between 0 and 1 or a percentage. However, power factors are sometimes conveyed as a percentage. For example, a power factor=0.5 is sometimes conveyed by engineers as being 50%.
Ideally, the power factor of a power converter system is 1.0, which means that the line voltage and consumed line current (input current) are both sinusoidal and in phase with each other. A power factor of a system is 0 when the current leads or lags the voltage by 90 degrees.
For two systems transmitting the same amount of real power to a load, the system with a lower power factor of the two will have higher circulating currents due to energy that returns to the source from energy storage in the load. Presence of the higher circulating currents in the system, as a result of a lower power factor, results in higher losses and reduced overall power transmission efficiency. Thus, a circuit having a lower power factor will have a higher apparent power and higher losses for the same amount of real power transfer.